1. Field of the Invention
The present invention relates to a resin laminate including a solid resin member and a foamed resin layer; and to a method of manufacturing same.
2. Description of the Art
FIG. 1 is a cross sectional view of a conventional resin laminate. A resin laminate is manufactured by applying an adhesive 220 onto either a skin 212 including a foam layer 211 or a foamed bead base 218 and securely adhering the skin 212 to the foamed bead base 218 by vacuum molding or press forming.
The application of the adhesive is time-consuming and uniform application of the adhesive is difficult. Uneven application of the adhesive 220 often causes irregularities or roughness on the surface of the skin 212 which may damage the ornamental capacity of the skin, as is demonstrated in FIG. 1. The irregularities on the surface of the foamed bead base 218 also cause roughness of the skin 212.
In another known method of manufacturing a resin laminate, a skin and a foamed bead base are each made of the same material, for example, polypropylene, and they are thermally adhered to each other during the process of vacuum forming. This method does not however, eliminate adverse effects of the roughness of the foamed bead base on the skin surface. Furthermore this method provides a relatively low adhering strength, especially on both ends of the foamed bead base where the temperature during the adhering process is relatively low. If the temperature is increased, however, the skin and the foamed bead base may be deformed.
Another technique to manufacture a resin laminate including a foam layer and a skin is disclosed in JAPANESE PATENT LAID-OPEN GAZETTE No. Sho-58-171921. This method includes the steps of vacuum forming a skin of a desirable shape, placing the skin in a mold of a forming device, piling resin foamed beads, which are preliminary expanded, upon the inner face of the skin in the mold and thermally expanding the resin foaming beads with steam to mold a reinforcing foam layer under the skin. Since the resin foaming beads generally have irregularities on their surface, it is impossible to produce a thin skin which will hide the irregularities and, as a result, the ornamental capacity of the skin is decreased. A thicker skin is therefore required to compensate for the irregularities of the resin forming beads, but the thicker skin increases the manufacturing cost.
Moreover, the resin foaming beads are only expanded over a narrow range of temperature. Even if the temperature of steam, the normal method of expansion, is slightly out of the suitable temperature range, the resin foaming beads may be insufficiently expanded or excessively molten such that they are deformed and hence, unacceptable. On the other hand, the skin is required to be partly molten on the surface such that it can be adhered to the foam layer. Even if the temperature range suitable for melting the skin is slightly different from the temperature range suitable for expanding the resin beads, the skin may be insufficiently molten or excessively molten, causing deformation. The materials which can be used for the skin are therefore limited to a very narrow range.
Conventionally, a resin laminate for automobile components includes a skin, a foam layer, and a resin base. In expanding the foam layer, a surface of the resin base as well as that of the skin are melted to adhere to the foam layer. The resin base, which is directly attached to the body of a vehicle, is required to have a sufficient strength. If the resin base is made of an olefin resin, such as polypropylene, the resin material should have a high glass transition point to assure the sufficient strength. If such a resin material having a high glass transition point is used for the resin base, however, there are no suitable resin foaming beads which have an expanding temperature close enough to the glass transition point to be acceptable in conjunction with such a resin.